Amino acid identity and/or position determine the proteasomal cleavage of the HLA-A*0201-restricted peptide tumor antigen MAGE-3271-279 (original) (raw)

The proteasome plays a crucial role in the proteolytic processing of antigens presented to T cells in the context of MHC class I molecules. However, the rules governing the specificity of cleavage sites are still largely unknown. We have previously shown that a CTL-defined antigenic peptide derived from the MAGE-3 tumor associated antigen (MAGE-3 271-279 , FLWGPRALV in one-letter code) is not presented at the surface of melanoma cell lines expressing the MAGE-3 protein. Using purified proteasome and MAGE-3 271-279 peptides extended at C-terminus by 6 amino acids, we had identified predominant cleavages after residues 278 and 280 but no detectable cleavage after residue Val 279 , the C-terminus of the antigenic peptide. In the present study, we have investigated the influence of Pro 275 , Leu 278 and Glu 280 on the proteasomal digestion of MAGE-3 271-285 substituted at these positions. We show that positions 278 and 280 are major proteasomal cleavage sites because they tolerate most amino acid substitutions. In contrast, the peptide bond after Val 279 is a minor cleavage site, influenced by both distal and proximal amino acid residues.